/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.view;

import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Properties;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.BeanUtils;
import org.springframework.context.ApplicationContext;
import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.PatternMatchUtils;
import org.springframework.web.servlet.View;

/**
 * Simple implementation of the {@link org.springframework.web.servlet.ViewResolver}
 * interface, allowing for direct resolution of symbolic view names to URLs,
 * without explicit mapping definition. This is useful if your symbolic names
 * match the names of your view resources in a straightforward manner
 * (i.e. the symbolic name is the unique part of the resource's filename),
 * without the need for a dedicated mapping to be defined for each view.
 *
 * <p>Supports {@link AbstractUrlBasedView} subclasses like {@link InternalResourceView}
 * and {@link org.springframework.web.servlet.view.freemarker.FreeMarkerView}.
 * The view class for all views generated by this resolver can be specified
 * via the "viewClass" property.
 *
 * <p>View names can either be resource URLs themselves, or get augmented by a
 * specified prefix and/or suffix. Exporting an attribute that holds the
 * RequestContext to all views is explicitly supported.
 *
 * <p>Example: prefix="/WEB-INF/jsp/", suffix=".jsp", viewname="test" ->
 * "/WEB-INF/jsp/test.jsp"
 *
 * <p>As a special feature, redirect URLs can be specified via the "redirect:"
 * prefix. E.g.: "redirect:myAction" will trigger a redirect to the given
 * URL, rather than resolution as standard view name. This is typically used
 * for redirecting to a controller URL after finishing a form workflow.
 *
 * <p>Furthermore, forward URLs can be specified via the "forward:" prefix.
 * E.g.: "forward:myAction" will trigger a forward to the given URL, rather than
 * resolution as standard view name. This is typically used for controller URLs;
 * it is not supposed to be used for JSP URLs - use logical view names there.
 *
 * <p>Note: This class does not support localized resolution, i.e. resolving
 * a symbolic view name to different resources depending on the current locale.
 *
 * <p><b>Note:</b> When chaining ViewResolvers, a UrlBasedViewResolver will check whether
 * the {@link AbstractUrlBasedView#checkResource specified resource actually exists}.
 * However, with {@link InternalResourceView}, it is not generally possible to
 * determine the existence of the target resource upfront. In such a scenario,
 * a UrlBasedViewResolver will always return View for any given view name;
 * as a consequence, it should be configured as the last ViewResolver in the chain.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @see #setViewClass
 * @see #setPrefix
 * @see #setSuffix
 * @see #setRequestContextAttribute
 * @see #REDIRECT_URL_PREFIX
 * @see AbstractUrlBasedView
 * @see InternalResourceView
 * @see org.springframework.web.servlet.view.freemarker.FreeMarkerView
 * @since 13.12.2003
 */
public class UrlBasedViewResolver extends AbstractCachingViewResolver implements Ordered {

    /**
     * Prefix for special view names that specify a redirect URL (usually
     * to a controller after a form has been submitted and processed).
     * Such view names will not be resolved in the configured default
     * way but rather be treated as special shortcut.
     */
    public static final String REDIRECT_URL_PREFIX = "redirect:";

    /**
     * Prefix for special view names that specify a forward URL (usually
     * to a controller after a form has been submitted and processed).
     * Such view names will not be resolved in the configured default
     * way but rather be treated as special shortcut.
     */
    public static final String FORWARD_URL_PREFIX = "forward:";


    @Nullable
    private Class<?> viewClass;

    private String prefix = "";

    private String suffix = "";

    @Nullable
    private String contentType;

    private boolean redirectContextRelative = true;

    private boolean redirectHttp10Compatible = true;

    @Nullable
    private String[] redirectHosts;

    @Nullable
    private String requestContextAttribute;

    /**
     * Map of static attributes, keyed by attribute name (String).
     */
    private final Map<String, Object> staticAttributes = new HashMap<>();

    @Nullable
    private Boolean exposePathVariables;

    @Nullable
    private Boolean exposeContextBeansAsAttributes;

    @Nullable
    private String[] exposedContextBeanNames;

    @Nullable
    private String[] viewNames;

    private int order = Ordered.LOWEST_PRECEDENCE;


    /**
     * Set the view class that should be used to create views.
     *
     * @param viewClass class that is assignable to the required view class
     *                  (by default, AbstractUrlBasedView)
     * @see AbstractUrlBasedView
     */
    public void setViewClass(@Nullable Class<?> viewClass) {
        if (viewClass != null && !requiredViewClass().isAssignableFrom(viewClass)) {
            throw new IllegalArgumentException("Given view class [" + viewClass.getName() +
                    "] is not of type [" + requiredViewClass().getName() + "]");
        }
        this.viewClass = viewClass;
    }

    /**
     * Return the view class to be used to create views.
     */
    @Nullable
    protected Class<?> getViewClass() {
        return this.viewClass;
    }

    /**
     * Return the required type of view for this resolver.
     * This implementation returns AbstractUrlBasedView.
     *
     * @see AbstractUrlBasedView
     */
    protected Class<?> requiredViewClass() {
        return AbstractUrlBasedView.class;
    }

    /**
     * Set the prefix that gets prepended to view names when building a URL.
     */
    public void setPrefix(@Nullable String prefix) {
        this.prefix = (prefix != null ? prefix : "");
    }

    /**
     * Return the prefix that gets prepended to view names when building a URL.
     */
    protected String getPrefix() {
        return this.prefix;
    }

    /**
     * Set the suffix that gets appended to view names when building a URL.
     */
    public void setSuffix(@Nullable String suffix) {
        this.suffix = (suffix != null ? suffix : "");
    }

    /**
     * Return the suffix that gets appended to view names when building a URL.
     */
    protected String getSuffix() {
        return this.suffix;
    }

    /**
     * Set the content type for all views.
     * <p>May be ignored by view classes if the view itself is assumed
     * to set the content type, e.g. in case of JSPs.
     */
    public void setContentType(@Nullable String contentType) {
        this.contentType = contentType;
    }

    /**
     * Return the content type for all views, if any.
     */
    @Nullable
    protected String getContentType() {
        return this.contentType;
    }

    /**
     * Set whether to interpret a given redirect URL that starts with a
     * slash ("/") as relative to the current ServletContext, i.e. as
     * relative to the web application root.
     * <p>Default is "true": A redirect URL that starts with a slash will be
     * interpreted as relative to the web application root, i.e. the context
     * path will be prepended to the URL.
     * <p><b>Redirect URLs can be specified via the "redirect:" prefix.</b>
     * E.g.: "redirect:myAction"
     *
     * @see RedirectView#setContextRelative
     * @see #REDIRECT_URL_PREFIX
     */
    public void setRedirectContextRelative(boolean redirectContextRelative) {
        this.redirectContextRelative = redirectContextRelative;
    }

    /**
     * Return whether to interpret a given redirect URL that starts with a
     * slash ("/") as relative to the current ServletContext, i.e. as
     * relative to the web application root.
     */
    protected boolean isRedirectContextRelative() {
        return this.redirectContextRelative;
    }

    /**
     * Set whether redirects should stay compatible with HTTP 1.0 clients.
     * <p>In the default implementation, this will enforce HTTP status code 302
     * in any case, i.e. delegate to {@code HttpServletResponse.sendRedirect}.
     * Turning this off will send HTTP status code 303, which is the correct
     * code for HTTP 1.1 clients, but not understood by HTTP 1.0 clients.
     * <p>Many HTTP 1.1 clients treat 302 just like 303, not making any
     * difference. However, some clients depend on 303 when redirecting
     * after a POST request; turn this flag off in such a scenario.
     * <p><b>Redirect URLs can be specified via the "redirect:" prefix.</b>
     * E.g.: "redirect:myAction"
     *
     * @see RedirectView#setHttp10Compatible
     * @see #REDIRECT_URL_PREFIX
     */
    public void setRedirectHttp10Compatible(boolean redirectHttp10Compatible) {
        this.redirectHttp10Compatible = redirectHttp10Compatible;
    }

    /**
     * Return whether redirects should stay compatible with HTTP 1.0 clients.
     */
    protected boolean isRedirectHttp10Compatible() {
        return this.redirectHttp10Compatible;
    }

    /**
     * Configure one or more hosts associated with the application.
     * All other hosts will be considered external hosts.
     * <p>In effect, this property provides a way turn off encoding on redirect
     * via {@link HttpServletResponse#encodeRedirectURL} for URLs that have a
     * host and that host is not listed as a known host.
     * <p>If not set (the default) all URLs are encoded through the response.
     *
     * @param redirectHosts one or more application hosts
     * @since 4.3
     */
    public void setRedirectHosts(@Nullable String... redirectHosts) {
        this.redirectHosts = redirectHosts;
    }

    /**
     * Return the configured application hosts for redirect purposes.
     *
     * @since 4.3
     */
    @Nullable
    public String[] getRedirectHosts() {
        return this.redirectHosts;
    }

    /**
     * Set the name of the RequestContext attribute for all views.
     *
     * @param requestContextAttribute name of the RequestContext attribute
     * @see AbstractView#setRequestContextAttribute
     */
    public void setRequestContextAttribute(@Nullable String requestContextAttribute) {
        this.requestContextAttribute = requestContextAttribute;
    }

    /**
     * Return the name of the RequestContext attribute for all views, if any.
     */
    @Nullable
    protected String getRequestContextAttribute() {
        return this.requestContextAttribute;
    }

    /**
     * Set static attributes from a {@code java.util.Properties} object,
     * for all views returned by this resolver.
     * <p>This is the most convenient way to set static attributes. Note that
     * static attributes can be overridden by dynamic attributes, if a value
     * with the same name is included in the model.
     * <p>Can be populated with a String "value" (parsed via PropertiesEditor)
     * or a "props" element in XML bean definitions.
     *
     * @see org.springframework.beans.propertyeditors.PropertiesEditor
     * @see AbstractView#setAttributes
     */
    public void setAttributes(Properties props) {
        CollectionUtils.mergePropertiesIntoMap(props, this.staticAttributes);
    }

    /**
     * Set static attributes from a Map, for all views returned by this resolver.
     * This allows to set any kind of attribute values, for example bean references.
     * <p>Can be populated with a "map" or "props" element in XML bean definitions.
     *
     * @param attributes a Map with name Strings as keys and attribute objects as values
     * @see AbstractView#setAttributesMap
     */
    public void setAttributesMap(@Nullable Map<String, ?> attributes) {
        if (attributes != null) {
            this.staticAttributes.putAll(attributes);
        }
    }

    /**
     * Allow Map access to the static attributes for views returned by
     * this resolver, with the option to add or override specific entries.
     * <p>Useful for specifying entries directly, for example via
     * "attributesMap[myKey]". This is particularly useful for
     * adding or overriding entries in child view definitions.
     */
    public Map<String, Object> getAttributesMap() {
        return this.staticAttributes;
    }

    /**
     * Specify whether views resolved by this resolver should add path variables to the model or not.
     * <p>>The default setting is to let each View decide (see {@link AbstractView#setExposePathVariables}.
     * However, you can use this property to override that.
     *
     * @param exposePathVariables <ul>
     *                            <li>{@code true} - all Views resolved by this resolver will expose path variables
     *                            <li>{@code false} - no Views resolved by this resolver will expose path variables
     *                            <li>{@code null} - individual Views can decide for themselves (this is used by the default)
     *                            </ul>
     * @see AbstractView#setExposePathVariables
     */
    public void setExposePathVariables(@Nullable Boolean exposePathVariables) {
        this.exposePathVariables = exposePathVariables;
    }

    /**
     * Return whether views resolved by this resolver should add path variables to the model or not.
     */
    @Nullable
    protected Boolean getExposePathVariables() {
        return this.exposePathVariables;
    }

    /**
     * Set whether to make all Spring beans in the application context accessible
     * as request attributes, through lazy checking once an attribute gets accessed.
     * <p>This will make all such beans accessible in plain {@code ${...}}
     * expressions in a JSP 2.0 page, as well as in JSTL's {@code c:out}
     * value expressions.
     * <p>Default is "false".
     *
     * @see AbstractView#setExposeContextBeansAsAttributes
     */
    public void setExposeContextBeansAsAttributes(boolean exposeContextBeansAsAttributes) {
        this.exposeContextBeansAsAttributes = exposeContextBeansAsAttributes;
    }

    @Nullable
    protected Boolean getExposeContextBeansAsAttributes() {
        return this.exposeContextBeansAsAttributes;
    }

    /**
     * Specify the names of beans in the context which are supposed to be exposed.
     * If this is non-null, only the specified beans are eligible for exposure as
     * attributes.
     *
     * @see AbstractView#setExposedContextBeanNames
     */
    public void setExposedContextBeanNames(@Nullable String... exposedContextBeanNames) {
        this.exposedContextBeanNames = exposedContextBeanNames;
    }

    @Nullable
    protected String[] getExposedContextBeanNames() {
        return this.exposedContextBeanNames;
    }

    /**
     * Set the view names (or name patterns) that can be handled by this
     * {@link org.springframework.web.servlet.ViewResolver}. View names can contain
     * simple wildcards such that 'my*', '*Report' and '*Repo*' will all match the
     * view name 'myReport'.
     *
     * @see #canHandle
     */
    public void setViewNames(@Nullable String... viewNames) {
        this.viewNames = viewNames;
    }

    /**
     * Return the view names (or name patterns) that can be handled by this
     * {@link org.springframework.web.servlet.ViewResolver}.
     */
    @Nullable
    protected String[] getViewNames() {
        return this.viewNames;
    }

    /**
     * Specify the order value for this ViewResolver bean.
     * <p>The default value is {@code Ordered.LOWEST_PRECEDENCE}, meaning non-ordered.
     *
     * @see org.springframework.core.Ordered#getOrder()
     */
    public void setOrder(int order) {
        this.order = order;
    }

    @Override
    public int getOrder() {
        return this.order;
    }

    @Override
    protected void initApplicationContext() {
        super.initApplicationContext();
        if (getViewClass() == null) {
            throw new IllegalArgumentException("Property 'viewClass' is required");
        }
    }


    /**
     * This implementation returns just the view name,
     * as this ViewResolver doesn't support localized resolution.
     */
    @Override
    protected Object getCacheKey(String viewName, Locale locale) {
        return viewName;
    }

    /**
     * Overridden to implement check for "redirect:" prefix.
     * <p>Not possible in {@code loadView}, since overridden
     * {@code loadView} versions in subclasses might rely on the
     * superclass always creating instances of the required view class.
     *
     * @see #loadView
     * @see #requiredViewClass
     */
    @Override
    protected View createView(String viewName, Locale locale) throws Exception {
        // If this resolver is not supposed to handle the given view,
        // return null to pass on to the next resolver in the chain.
        if (!canHandle(viewName, locale)) {
            return null;
        }

        // Check for special "redirect:" prefix.
        if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
            String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
            RedirectView view = new RedirectView(redirectUrl,
                    isRedirectContextRelative(), isRedirectHttp10Compatible());
            String[] hosts = getRedirectHosts();
            if (hosts != null) {
                view.setHosts(hosts);
            }
            return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
        }

        // Check for special "forward:" prefix.
        if (viewName.startsWith(FORWARD_URL_PREFIX)) {
            String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
            InternalResourceView view = new InternalResourceView(forwardUrl);
            return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
        }

        // Else fall back to superclass implementation: calling loadView.
        return super.createView(viewName, locale);
    }

    /**
     * Indicates whether or not this {@link org.springframework.web.servlet.ViewResolver} can
     * handle the supplied view name. If not, {@link #createView(String, java.util.Locale)} will
     * return {@code null}. The default implementation checks against the configured
     * {@link #setViewNames view names}.
     *
     * @param viewName the name of the view to retrieve
     * @param locale   the Locale to retrieve the view for
     * @return whether this resolver applies to the specified view
     * @see org.springframework.util.PatternMatchUtils#simpleMatch(String, String)
     */
    protected boolean canHandle(String viewName, Locale locale) {
        String[] viewNames = getViewNames();
        return (viewNames == null || PatternMatchUtils.simpleMatch(viewNames, viewName));
    }

    /**
     * Delegates to {@code buildView} for creating a new instance of the
     * specified view class. Applies the following Spring lifecycle methods
     * (as supported by the generic Spring bean factory):
     * <ul>
     * <li>ApplicationContextAware's {@code setApplicationContext}
     * <li>InitializingBean's {@code afterPropertiesSet}
     * </ul>
     *
     * @param viewName the name of the view to retrieve
     * @return the View instance
     * @throws Exception if the view couldn't be resolved
     * @see #buildView(String)
     * @see org.springframework.context.ApplicationContextAware#setApplicationContext
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     */
    @Override
    protected View loadView(String viewName, Locale locale) throws Exception {
        AbstractUrlBasedView view = buildView(viewName);
        View result = applyLifecycleMethods(viewName, view);
        return (view.checkResource(locale) ? result : null);
    }

    /**
     * Creates a new View instance of the specified view class and configures it.
     * Does <i>not</i> perform any lookup for pre-defined View instances.
     * <p>Spring lifecycle methods as defined by the bean container do not have to
     * be called here; those will be applied by the {@code loadView} method
     * after this method returns.
     * <p>Subclasses will typically call {@code super.buildView(viewName)}
     * first, before setting further properties themselves. {@code loadView}
     * will then apply Spring lifecycle methods at the end of this process.
     *
     * @param viewName the name of the view to build
     * @return the View instance
     * @throws Exception if the view couldn't be resolved
     * @see #loadView(String, java.util.Locale)
     */
    protected AbstractUrlBasedView buildView(String viewName) throws Exception {
        Class<?> viewClass = getViewClass();
        Assert.state(viewClass != null, "No view class");

        AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
        view.setUrl(getPrefix() + viewName + getSuffix());

        String contentType = getContentType();
        if (contentType != null) {
            view.setContentType(contentType);
        }

        view.setRequestContextAttribute(getRequestContextAttribute());
        view.setAttributesMap(getAttributesMap());

        Boolean exposePathVariables = getExposePathVariables();
        if (exposePathVariables != null) {
            view.setExposePathVariables(exposePathVariables);
        }
        Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
        if (exposeContextBeansAsAttributes != null) {
            view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
        }
        String[] exposedContextBeanNames = getExposedContextBeanNames();
        if (exposedContextBeanNames != null) {
            view.setExposedContextBeanNames(exposedContextBeanNames);
        }

        return view;
    }

    /**
     * Apply the containing {@link ApplicationContext}'s lifecycle methods
     * to the given {@link View} instance, if such a context is available.
     *
     * @param viewName the name of the view
     * @param view     the freshly created View instance, pre-configured with
     *                 {@link AbstractUrlBasedView}'s properties
     * @return the {@link View} instance to use (either the original one
     * or a decorated variant)
     * @see #getApplicationContext()
     * @see ApplicationContext#getAutowireCapableBeanFactory()
     * @see org.springframework.beans.factory.config.AutowireCapableBeanFactory#initializeBean
     * @since 5.0
     */
    protected View applyLifecycleMethods(String viewName, AbstractUrlBasedView view) {
        ApplicationContext context = getApplicationContext();
        if (context != null) {
            Object initialized = context.getAutowireCapableBeanFactory().initializeBean(view, viewName);
            if (initialized instanceof View) {
                return (View) initialized;
            }
        }
        return view;
    }

}
